Top up Netflix gift card?

I bought a Netflix voucher card a long time ago. It cost 15 euro. I downloaded netflix and I was deducted 7.99 euro from the voucher. Now I have 7.01 euro from my voucher card but I need at least 7.99 euro to buy Netflix for another month. Can I top up a voucher? Can I top up 98 cents on my voucher and how? Or is the money gone?

Buy another card and use both.